Low- Voltage discharge lamp and its manufacturing method

ABSTRACT

A low-pressure discharge lamp having a tubular glass lamp vessel  10,  on an outer surface of which conductor layers are formed as electrodes  21  and  26.  The ultrasonic solder dipping layers  31  and  36  are formed at both ends of the vessel  10  as conductor layers. The end surfaces of the glass lamp vessel are blasted and ultrasonic solder dipping layers are formed on the blasted surfaces  41  and  46  by ultrasonic solder dipping. Conductor layers forme external electrodes  21  and  26,  which are in contact with the glass surface more strongly. A low-pressure discharge lamp having the conductor layers of a uniform thickness can be mass-produced at low cost.

FIELD OF THE INVENTION

The present invention relates to a low-pressure discharge lamp and amethod for manufacturing it.

BACKGROUND OF THE INVENTION

A dielectric barrier discharge type low-pressure discharge lamp havingan electrode on the outer surface of a tubular glass lamp vessel (EEFL)is known as an example which is described in the laid-openJapanese-utility model application Shou 61-126559, for example. Thislow-pressure discharge lamp is charged with ionizable filler such asrare gas or mixed gas of mercury and rare gas inside a tubular glasslamp vessel with both ends sealed. On the inner wall surface of thetubular glass lamp vessel, a phosphor layer is formed as necessary. Onthe outer surfaces of both ends of the tubular glass lamp vessel,external electrodes are arranged.

The external electrodes are composed of, for example, a metallic tapemade of aluminum foil and a conductive adhesive for forming anelectrically conductive layer and coiled lead wires connected to themetallic tape, which acts as a metal fitting for supplying thelow-pressure discharge lamp with an electric power. Here, the coiledlead wires are made contact with the metallic tapes by their ownelasticity.

The low-pressure discharge lamp having such a structure has an advantagethat no electrode is provided in the tubular glass lamp vessel, so thatno electrode consumption is caused and the life is long. However, sincethe diameter of the tubular glass lamp vessel is very small such asabout 3 mm, a complicated machine is required to apply the metallic tapeon the tubular glass lamp vessel with high dimensional accuracy and itis difficult to manufacture the discharge lamps in mass production.

Further, in an electrode using such a metallic tape, a power loss iscaused in the conductive adhesive made of acrylic resin when a currentflows through the metallic tape, and there is a defect of increasing inthe power consumption of the lamp.

Furthermore, since the conductive adhesive has low heat resistance, itis partially carbonized due to generation of heat when the currentflows, and the resistance of the part is reduced, where the current isconcentrated. As a result, a problem arises that intense heat isgenerated, and the tubular glass lamp vessel is partially fused to forma hole.

According to embodiments of the present invention, the low-pressuredischarge lamp having an electrode using a conventional metallic tape isprovided, with which such technical problems as high power consumptionor forming the hole of are solved and which is capable of adopting amanufacturing method for realizing mass production at low cost.

SUMMARY OF THE INVENTION

The low-pressure discharge lamp according to the present invention ischaracterized in that an end portion of a tubular glass lamp vessel isdipped in a solder bath in which a solder material having good contactwith a glass surface is fused, and thus an electric conductor layer ofan external electrode is formed. As a solder material having a goodcontact with the glass surface, the conductor layer becomes adhesive andstrong, when any one of tin, an alloy of tin and indium or an alloy oftin and bismuth is used as a main component. The dischargecharacteristic of the lamp having the conductor layer is stabilized, andthe life span of the lamp is lengthened. Further, when the soldermaterial contains at least one of antimony, zinc or aluminum as anadditive, the surface of the tubular glass lamp vessel and the conductorlayer have good contact with each other, with which the conductor layeris hardly separated from the surface of the tubular glass lamp vessel.Thus the discharge characteristic is stabilized and the life span of thelamp is lengthened. Moreover, when the solder dipping method is adoptedto form the conductor layer, mass production can be realized and thecost can be decreased.

Further, the low-pressure discharge lamp according to the presentinvention is characterized in that the end portion of the tubular glasslamp vessel is dipped into an ultrasonic solder bath in which a soldermaterial is fused, thus a conductor layer of an external electrode isformed. When any one of tin, an alloy of tin and indium, or an alloy oftin and bismuth is used as a main component of the solder material, theconductor layer becomes adhesive and strong. Thus the dischargecharacteristic of the lamp is stabilized, and the life span of the lampis lengthened.

Since the conductor layer of the external electrode is formed by dippinginto the ultrasonic solder bath in the low-pressure discharge lampaccording to the present invention, an even layer with a uniformthickness is obtained and a highly efficient low-pressure discharge lampcan be realized. Moreover, mass production can be realized and the costcan be decreased by applying the ultrasonic solder dipping method toforming the conductor layer.

Furthermore, the low-pressure discharge lamp according to the presentinvention is characterized in that the surface of the end portion of thetubular glass lamp vessel is blasted and is then dipped into theultrasonic solder bath, in which the solder material is fused, to formthe conductor layer of the external electrode.

In the low-pressure discharge lamp according to the present invention,the conductor layer of the external electrode having an even layer witha uniform thickness is formed by dipping the end portion of the tubularglass lamp vessel into the ultrasonic solder bath. Moreover, theconductor layer is hardly separated from the tubular glass lamp vesseland a highly efficient low-pressure discharge lamp can be provided,since the conductor layer is formed on the blasted surface by ultrasonicsolder dipping. In addition, mass production can be realized and thecost can be decreased by applying the ultrasonic solder dipping method.

Further, the manufacture of the low-pressure discharge lamps using thesolder containing no lead does not give any adverse effect to theenvironment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross sectional view of the dielectric barrierdischarge type low-pressure discharge lamp according to a firstembodiment of the present invention.

FIG. 2 is an axial cross sectional view of the dielectric barrierdischarge type low-pressure discharge lamp according to a secondembodiment of the present invention.

FIG. 3 is an axial cross sectional view of the dielectric barrierdischarge type low-pressure discharge lamp according to a thirdembodiment of the present invention.

FIG. 4 is an axial cross sectional view of the dielectric barrierdischarge type low-pressure discharge lamp according to a fourthembodiment of the present invention.

FIG. 5 is an axial cross sectional view of the dielectric barrierdischarge type low-pressure discharge lamp according to a fifthembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The embodiments according to the present invention will be now explainedwith reference to the accompanying drawings. FIG. 1 shows the structureof a dielectric barrier discharge type low-pressure discharge lamp 11according to a first embodiment of the present invention. In thelow-pressure discharge lamp 11, a tubular glass lamp vessel 10 is formedwith borosilicate glass, having an outer diameter of 2.6 mm, an innerdiameter of 2.0 mm, and a total length of 350 mm. The tubular glass lampvessel 10 is charged with mixed gases of neon and argon at a chargepressure of 60 Torr (composition ratio of neon/argon is 90 mol %/10 mol%). Further, the tubular glass lamp vessel is also charged with 3 mg ofmercury.

On outer surfaces of both ends of the tubular glass lamp vessel 10,solder dipping layers 30 and 35 are formed respectively as conductorlayers of external electrodes 21 and 26. On an inner peripheral wall ofthe tubular glass lamp vessel 10 excluding the parts where the externalelectrodes 21 and 26 are installed, a phosphor layer 70 composed of aphosphor is formed emitting lights having three different wave lengths,i.e. R, G and B. The thickness of the phosphor layer 70 is about 20 μm.

The solder dipping layers 30 and 35 are formed by dipping the ends ofthe tubular glass lamp vessel 10 in a solder bath at about 350° C. wheretin, zinc, aluminum, and antimony are fused for about 30 seconds. Thethickness of the formed solder dipping layers 30 or 35 is about 5 μm andthe length of the solder dipping layers 30 or 35 is about 20 mm. Coiledlead wires 51 and 56 are provided at the both ends of the tubular glasslamp vessel 10 where the solder dipping layers 30 and 35 are formed,which make contact with the solder dipping layers 30 and 35 with theirown an elastic force.

The inventors of the patent application examined various materials forthe solder material and finally confirmed that a uniform and adhesivedeposit is formed on the surface of the tubular glass lamp vessel 10 byany one of solder materials of tin, an alloy of tin and indium, or analloy of tin and bismuth. Further, the solder material containing as anadditive at least one of antimony, zinc, or aluminum makes the conductorlayer to be in good contact with the surface of the tubular glass lampvessel, thereby making the conductor layer to be hardly separated, andprovides the solder dipping layers 30 and 35 having a stable dischargecharacteristic. Namely, the solder materials containing tin and at leastone of antimony, zinc, or aluminum as an additive also realize goodadhesion.

Similarly, solder materials containing an alloy of tin and indium or analloy of tin and bismuth including respectively at least one ofantimony, zinc or aluminum as an additive also realize good adhesion aswell as lower their melting point so that the solder dipping can beeasily carried out. Further, a solder electrode can be formed, whosesurface oxidation hardly proceeds, thereby forming a stable conductiveelectrode, when aluminum is added to tin+zinc+antimony.

Further, in the dielectric barrier discharge type low-pressure dischargelamp according to the embodiment, the voltage at the electrode hardlydrops, so that the lamp voltage can be lowered compared with theconventional dielectric barrier discharge type low-pressure dischargelamp having an electrode made of the metallic tape. For example, thelamp voltage at a lamp current of 4 mA and a lighting frequency of 45kHz is 1940 Vrms in the conventional lamp and is 1790 Vrms in the lampaccording to the embodiment of the present invention.

The experiment of the inventors of the present invention revealed that auniform solder layer cannot be formed on the surface of the vesselbecause some portions of the surface of the tubular glass lamp vessel 10remained uncovered when the both ends of a tubular glass lamp vessel aredipped into a solder bath, in which an alloy of tin and copper is fusedto form a deposit. Here, the alloy of tin and copper is widely used as asolder material containing no lead. Further, for a solder materialcomposed of an alloy of tin, copper and silver, the similar results areobtained. When such a low-pressure discharge lamp 18 is kept on for manyhours, a current is excessively concentrated on a part of the solderdipping layer, resulting an over heating of a part of the end portionsof the tubular glass lamp vessel 10 and resulting in forming a hole, andfinally a problem may arise that the lamp 18 is not kept on.

However, the solder dipping layers 30 and 35 formed on the surface ofthe glass lamp vessel 10 according to the embodiment of the presentinvention are uniform in thickness and adhesive, so that the problem ofexposing the surface of the glass lamp vessel 10, which forms a base, isprevented.

FIG. 2 shows a structure of the dielectric barrier discharge typelow-pressure discharge lamp 11 according to the second embodiment of thepresent invention. The lamp 11 shown in the drawing has basically thesame configuration as that of the discharge lamp 11 shown in FIG. 1except for some portions. Therefore, the same numerals are assigned tothe same parts and some different parts from the first embodiment willbe mainly explained below. In the lamp 11, ultrasonic solder dippinglayers 31 and 36 are formed on outer surfaces at both ends of thetubular glass lamp vessel 10. These ultrasonic solder dipping layers 31and 36 are respectively used as conductor layers constituting theexternal electrodes 21 and 26.

Ultrasonic solder dipping, as is generally known, is a method forplating while giving ultrasonic vibration to fused solder in a bath withan ultrasonic vibrator installed in the bath. In this embodiment, thesame solder material as in the first embodiment is used and theultrasonic vibrator operates at a vibration frequency of 20 kHz. Bothends of the tubular glass lamp vessel 10 are dipped in the fused solderbath at 230° C. for about 30 seconds. Further, KDB-100 ultrasonic solderbath is used, which is manufactured by Kuroda Technology Co., Ltd.

The solder dipping layers 31 and 36 thus formed, has a thickness of 5 μmand a length of 20 mm in the axial direction of the tube as is the casewith the first embodiment. The dipping layers 31 and 36 formed bydipping the tube ends into the ultrasonic solder bath have a moreuniform thickness than that of the solder dipping layers 30 and 35formed in a regular solder bath and are more adhesive to the surface ofthe tubular glass lamp vessel 10 as described later.

Next, the dielectric barrier discharge type low-pressure discharge lamp11 according to the third embodiment of the present invention will beexplained referring to FIG. 3. The dielectric barrier discharge typelow-pressure discharge lamp 11 shown in the drawing also has the sameconfiguration as that of the discharge lamp 11 shown in FIG. 2 as thesecond embodiment except for some parts thereof. Therefore, the samenumerals are assigned to the same parts and the different parts from thesecond embodiment will be mainly explained below. In the discharge lamp11 shown in FIG. 3, the outer surfaces of both ends of the tubular glasslamp vessel 10 are blasted to have rough surfaces. On blasted surfaces41 and 46, thus formed, the ultrasonic solder dipping layers 31 and 36are formed. The blasting process is performed, for example, by rotatingthe tubular glass lamp vessel 10 around the tube axis and spraying analumina abrasive material on the rotating tubular glass lamp vessel 10.The blasting process can be performed by chemical etching using afluorine acid. Both ends of the tubular glass lamp vessel 10 subjectedto the blasting process are dipped into the ultrasonic solder bath underthe same condition as that of the second embodiment and thus theultrasonic solder dipping layers 31 and 36 are formed.

When the surface of the glass vessel 10 is turned into the roughsurfaces 41 and 46 applying the blasting process described, the contactarea between the ultrasonic solder dipping layers 31 and 36 and theglass surface of the tubular glass lamp vessel 10 is expanded and thusthe ultrasonic solder dipping layers 31 and 36 can be made hardlyseparable.

To inspect the adhesion or separability between the ultrasonic solderdipping layers and the surface of the tubular glass lamp vesselaccording to the embodiment of the present invention, the inventorsformed solder dipping layers using regular solder as a comparisonexample and executed the comparison experiment between the comparisonexample and the ultrasonic solder dipping layers according to the secondand the third embodiment described above. Specifically, a blastedtubular glass lamp vessel and a non-blasted tubular glass lamp vesselare dipped into the solder bath to form comparison examples 1 and 2respectively. In the solder bath, the alloy of tin and copper is fused,which is used in the aforementioned experiment by the inventors. Forminglattice scratches are formed at intervals of 1 mm on the comparisonexamples 1 and 2 as well as the ultrasonic solder dipping layersaccording to the embodiments 2 and 3 of the present invention, a heatcycle test is executed and then the separation test is executed using acellulose tape. The test results are given in Table 1. Further, in theheat cycle, keeping each sample in an environment of 80° C. for 0.5hours and then keeping it in an environment of −30° C. for 0.5 hours,which constitute one cycle. TABLE 1 0 cycle 100 cycles 200 cycles 500cycles Electroless N.G. (even plated non electrode scratched (not partblasted) completely (comparison separated) example 1) Electroless OK OKN.G. (even plated non electrode scratched (blasted) part (comparisoncompletely example 2) separated) Ultrasonic OK OK OK OK solder electrode(not blasted) (embodiment 2) Ultrasonic OK OK OK OK solder electrode(blasted) (embodiment 3)

From the results of the heat cycle test, it is confirmed that theexternal electrodes made of the ultrasonic solder dipping layersaccording to the embodiments of the present invention are stronger inthe heat cycle test than the external electrodes made by the regularsolder bath dipping method using an alloy of tin and copper or an alloyof tin, copper, and silver as a solder material.

Further, it is found from the difference between the embodiment 2 andthe embodiment 3 that the contact area between the surface of the glasslamp vessel and the ultrasonic solder dipping layer is extended and theadhesive strength can be increased by making the smooth surface of theglass lamp vessel 10 is blasted to make it uneven as in the embodiment 3and by forming an ultrasonic solder layer on the part blasted. Namely,by the blasting process, stronger and hardly separable externalelectrodes can be formed.

FIGS. 4 and 5 are drawings showing a fourth and a fifth embodimentsaccording to the dielectric barrier discharge type low-pressuredischarge lamp of the present invention. In a low-pressure dischargelamp 12 shown in FIG. 4, the blasted surfaces 41 and 46 are formed onthe outer surfaces of both ends of the tubular glass lamp vessel 10,similarly to the third embodiment shown in FIG. 3, and the ultrasonicsolder dipping layers 31 and 36 are formed on the surfaces thereof.Furthermore, a metal oxide layer 71 such as aluminum oxide, yttriumoxide, or zinc oxide is formed on a phosphor layer 70 in the tubularglass lamp vessel 10 and on the glass surfaces inside the externalelectrodes 21 and 26.

In the low-pressure discharge lamp 12 having such a construction, theultrasonic solder dipping method is adopted, thus mass production of ahighly efficient low-pressure discharge lamp can be realized at a lowprice as in the low-pressure discharge lamp 11 according to the secondembodiment. Furthermore, according to the embodiment, silver consumptiondue to adsorption of mercury into the phosphor layer 70 in the glasslamp vessel 10 can be suppressed and silver consumption due to entry ofsilver into the glass can be prevented. Thus a life span of the lamp canbe lengthened.

Next, in a low-pressure discharge lamp 13 shown in FIG. 5, the blastedsurfaces 41 and 46 are formed on the outer surfaces of both ends of thetubular glass lamp vessel 10, and the ultrasonic solder dipping layers31 and 36 are formed as external electrodes 21 and 26 on the surfacesthereof, as in the third embodiment. Further, a metal oxide layer 72such as aluminum oxide, yttrium oxide, or zinc oxide is formed betweenthe inner surface of the tubular glass lamp vessel 10 and the phosphorlayer 70 and on the glass surfaces inside the external electrodes 21 and26.

In the low-pressure discharge lamp 13 having such a construction, theultrasonic solder dipping method is adopted, thus mass production of ahighly efficient low-pressure discharge lamp can be realized at a lowprice similarly to the low-pressure discharge lamp 11 of the secondembodiment. Furthermore, according to the embodiment, silver consumptiondue to entry of silver into the glass surface of the tubular glass lampvessel 10 can be prevented and a life span can be lengthened.

Further, in the fourth and fifth embodiments, the case using thelow-pressure discharge lamp 11 according to the second embodiment isexplained. However, it is needless to say that the low-pressuredischarge lamp 11 of the first or third embodiment may be used.

The present invention is not limited to the aforementioned embodimentsand can be modified variously. For example, the coiled lead wires 51 and56 are installed on the both ends of the tubular glass lamp vessel 10,on which the solder dipping layers 30 and 35 or the ultrasonic solderdipping layers 31 and 36 are formed. However, they may not be alwayscoiled lead wires if conductors can make contact with the solder dippinglayers.

As explained above using various embodiments, the low-pressure dischargelamp according to the present invention, conductor layers composed of auniform and even metal deposit can be formed as external electrodes 21and 26 of the tubular glass lamp vessel 10. Further, the blasted endsurfaces 41 and 46 of the tubular glass lamp vessel 10 are dipped intothe solder bath, thus conductor layers very hardly separable from thetubular glass lamp vessel 10 can be formed. Therefore, a highlyefficient low-pressure discharge lamp having a stable dischargecharacteristic at low power consumption can be obtained. Moreover, itcan be manufactured by a comparatively easy art such as solder dipping,so that mass production can be realized and the cost of the low-pressuredischarge lamp can be reduced.

1. A low-pressure discharge lamp comprising a tubular glass lamp vesselon an outer surface of which a conductor layer is formed as anelectrode, wherein the conductor layer is a solder dipping layer formedby solder dipping and the solder dipping layer has a main component ofany one of tin, an alloy of tin and indium, or an alloy of tin andbismuth.
 2. A low-pressure discharge lamp according to claim 1, whereinthe solder dipping layer contains at least one of antimony, zinc, oraluminum as an additive.
 3. A low-pressure discharge lamp according toclaim 2, wherein a part of a surface of the tubular glass lamp vessel,where the solder dipping layer is formed, is blasted.
 4. A low-pressuredischarge lamp comprising a tubular glass lamp vessel on an outersurface of which a conductor layer is formed as an electrode, where inthe conductor layer is an ultrasonic solder dipping layer formed byultrasonic solder dipping.
 5. A low-pressure discharge lamp according toclaim 4, wherein the ultrasonic solder dipping layer has a maincomponent of any one of tin, an alloy of tin and indium, or an alloy oftin and bismuth.
 6. A low-pressure discharge lamp according to claim 5,wherein the ultrasonic solder dipping layer contains at least one ofantimony, zinc, or aluminum as an additive.
 7. A low-pressure dischargelamp according to claim 6, wherein a part of a surface of the tubularglass lamp vessel where the ultrasonic solder dipping layer is formed isblasted.
 8. A low-pressure discharge lamp according to claim 7, whereinthe ultrasonic solder dipping layer contains no lead component.
 9. Amethod for manufacturing a low-pressure discharge lamp, comprising stepsof: preparing a fused solder bath having a main component of either oneof an alloy of tin and indium or an alloy of tin and bismuth, dipping anend of a tubular glass lamp vessel into the fused solder bath, andforming solder dipping layers on the end of the tubular glass lampvessel used for an external electrode.
 10. A method for manufacturing alow-pressure discharge lamp according to claim 9, further comprising astep of blasting a surface of the end of the tubular glass lamp vesselbefore dipping the ends of the tubular glass lamp vessel into the fusedsolder bath.
 11. A method for manufacturing a low-pressure dischargelamp according to claim 10, wherein the fused solder contains at leastone of antimony, zinc, or aluminum as an additive.
 12. A method formanufacturing a low-pressure discharge lamp according to claim 11,wherein the fused solder contains no lead component.
 13. A method formanufacturing a low-pressure discharge lamp, comprising steps of:dipping an end of a tubular glass lamp vessel into an ultrasonic solderbath, and forming an ultrasonic solder dipping layer on an end of thetubular glass lamp vessel used for an external electrode.
 14. A methodfor manufacturing a low-pressure discharge lamp according to claim 13,wherein the ultrasonic solder has a main component of any one of tin, analloy of tin and indium or an alloy of tin and bismuth.
 15. A method formanufacturing a low-pressure discharge lamp according to claim 14,wherein the ultrasonic solder contains at least one of antimony, zinc oraluminum as an additive.
 16. A method for manufacturing a low-pressuredischarge lamp according to claim 15, wherein the ultrasonic soldercontains no lead component.
 17. A method for manufacturing alow-pressure discharge lamp, comprising steps of: blasting a surface ofan end of a tubular glass lamp vessel, and dipping the end of thetubular glass lamp vessel into an ultrasonic solder bath to form anultrasonic solder dipping layer used for external electrodes.
 18. Amethod for manufacturing a low-pressure discharge lamp according toclaim 17, wherein the ultrasonic solder has a main component of any oneof tin, an alloy of tin and indium or an alloy of tin and bismuth.
 19. Amethod for manufacturing a low-pressure discharge lamp according toclaim 18, wherein the ultrasonic solder contains at least one ofantimony, zinc or aluminum as an additive.
 20. A method formanufacturing a low-pressure discharge lamp according to claim 19,wherein the ultrasonic solder contains no lead component.